1. Data reliability on optical discs Mladen Tušek Filozofski fakultet, Ivana Lučića 3, Zagreb Hrvatska mladentusek@yahoo.com mladentusek@yahoo.com

2. Introduction Optical discs suitable for preserving data: CD650 or 700 MB DVD4,7 or 9 GB HD DVD 15 or 30 GB Blu-Ray 25 or 50 GB

4. Long term data preservation on optical discs Physical damage Chemical damage -chemical layer “Phthalocyanine” -reflexive gold layer

5. Identification of media Identification of disc manufacturer Identification of chemical layer Other relevant information about optical disc

8. Analysis and data recovery Disc reading speed as indication of data status on discs chemical layer Aging of chemical layer causing data loss on all optical discs of the same manufacturer Unequal quality of chemical layer causes data loss on one or more optical discs

12. Conclusion Using quality discs, two of them with different chemical layer and manufacturer Parallel data writing on two computers with two different data recorders (different manufacturers: Plextor and Pioneer, for example). Low speed recording (4x) and mandatory data verification after recording After data recording test readability of recorded disc in different optical devices

13. After one recording session and before erasing source data make readability test During archiving process in regular intervals (every 6 months) check readability using random method In case of problem use specialized applications and copy content of optical disc before irreversible data loss occur

14. Thank You